1. Field of the Invention
The present invention concerns magnetic laminations used in particular in the manufacture of electric motor stators.
2. Description of the Prior Art
As is well known, to limit Eddy current losses, magnetic parts of electrical devices such as motors, generators and transformers are made by assembling mutually insulated magnetic laminations.
At present, the silicon laminations used in the manufacture of welded electric motor stators, for example, are insulated by a phosphate varnish; the stators have to undergo a stress relieving treatment at 600.degree. C. which "thins" the insulation. To prevent this thinning loosening the laminations it is necessary to bring it about before assembling and welding the laminations. This additional operation increases the manufacturing cost of the stators.
An object of the present invention is to provide a lamination with insulation that is not "thinned" at a temperature of 600.degree. C.
It is hardly possible, with the lamination insulating methods used at present, to obtain a layer of insulation thicker than about 2 microns. The increasing operating frequencies of electric motors, which lead to an increase in the Eddy currents, require enhanced insulation. The thickness of 2 microns proves insufficient and an insulation layer thickness of around 5 microns to 10 microns is needed; also, this layer must be highly regular, with no "misses" on the lamination.
Another object of the invention is to define a method of producing an insulative layer allowing regular and uniform growth to thicknesses of up to 10 microns.